OFFSET
1,1
EXAMPLE
7531 is in the sequence because it is semiprime 7531 = 17*443 and 7-5 = 5-3 = 3-1 = 2.
97531 is in the sequence because it is semiprime 97531 = 7*13933 and 9-7 = 7-5 = 5-3 = 3-1 = 2.
MATHEMATICA
Sort[Flatten[Table[Select[FromDigits/@Partition[Range[9, 0, -2], n, 1], PrimeOmega[#]==2 &], {n, 1000}]]]
PROG
(PARI) for(d=1, 5, for(s=1, 11-2*d, t=sum(i=1, d, (s-2+2*i)*10^i)/10; if(bigomega(t)==2, print1(t", ")))) \\ Charles R Greathouse IV, Jul 16 2014
CROSSREFS
KEYWORD
nonn,base,easy,fini,full
AUTHOR
Vincenzo Librandi, Jul 10 2014
EXTENSIONS
a(1), a(2), a(4) from Charles R Greathouse IV, Jul 16 2014
STATUS
approved